Environmentalists who have fought loggers for generations have a surprising new strategy to save California’s storied old-growth redwood forests: Logging.

Save the Redwoods League, a venerable San Francisco organization that has preserved more than 214,000 acres of redwood forest since it was founded in 1918, is embarking on a $5 million plan to thin out 10,000 acres of redwoods, Douglas fir, tan oaks and other trees. The logging will begin at Redwood National Park and Del Norte Coast Redwoods State Park near the Oregon border over the next five years. After that, the group plans to thin forests in nearby Jedediah Smith and Prairie Creek Redwoods state parks.

Many of the spots under consideration were heavily logged decades ago before they were purchased and added to the parks, the league says. And cutting down the thinner trees — including those planted by loggers too densely as part of commercial reseeding operations in the 1960s — will restore more natural conditions, and reduce competition for sunlight and water, helping regular-sized redwoods grow faster into majestic old-growth giants.

But chainsaws in beloved redwood parks? Will the public go for it?

“It’s about allowing the younger forests to grow more effectively,” said Sam Hodder, president of Save the Redwoods League. “Right now in some of these places all the trees are crowding each other out.”

Many of California’s old-growth redwoods — the world’s tallest living things that can grow to more than 300 feet high and live 2,000 years — were cut down between the 1800s and the 1970s for decks, paneling, and even fence posts and railroad ties. Modern environmental laws and the creation of public parks ended it. Today, nearly all redwood lumber sold in stores is from second-and-third growth younger trees. Only about 5 percent of the original old-growth acreage remains, and nearly all of that is preserved in parks.

The new task for this century, Hodder said, is to restore landscapes that were logged but now exist in parks in a damaged, unnatural state.

That means removing old logging roads, restoring streams to bring back salmon and other fish, and doing everything to help second-and-third growth redwood trees get bigger, he said. On April 27, the league is scheduled to sign an agreement with the California state parks department and the National Park Service to allow for “restoration forestry” funded by the league as a way to undo the damage from industrial logging and recreate forests that are more natural.

The project in Humboldt and Del Norte counties “aligns the public and private sectors to take the next big steps towards restoring these cherished public landscapes. It is a great investment in our future,”said Steve Mietz, superintendent of Redwood National Park.

All four parks involved together have about 120,000 acres of forests. Of those, about 40,000 acres is old-growth redwood, and the other 80,000 acres are in formerly logged areas that project planners hope to thin and restore in the coming decades. Most of the trees cut down will be Douglas fir, with some second-growth redwood and hardwoods like tan oak, said Paul Ringold, a forest ecologist and chief program officer of the Save the Redwoods League. Roughly 30 to 70 percent of the trees will be taken out in the 10,000 acres treated between now and 2022, he said, and in some cases, sold to timber companies.

“These stands are a legacy of clear-cut logging,” Ringgold said. “We want to restore these areas as close as we can to the way they were pre-logging.”

But not everyone is rushing to embrace the project, which is called “Redwoods Rising.”

“I do have concerns when organizations who have historically been involved in the preservation of our old growth redwoods and our parks get into the business of logging. I’d like to see more details,” said Jodi Frediani, a longtime Santa Cruz County logging activist.

Frediani said she supports the removal of old logging roads and efforts the league is taking to study the impacts of climate change on redwood and Giant Sequoia forests. But she noted that the league has very few specifics about the new thinning projects on its website. And in any logging operation, even well-meaning ones, she added, heavy equipment can damage the forests and there is pressure to cut down larger trees, which are worth more money than thin ones.

“I find it a very slippery slope to have timber operations in state and national parks,” she said.

Hodder noted that in a natural old-growth forest there are about 200 trees per acre. In some forests that were clear cut and reseeded, there are 10 times that amount now. Redwood National Park already has done some thinning, he noted, to help restore areas that were purchased by the federal government from logging companies after the companies clear cut the biggest, oldest trees.

Under the organization’s plan, an environmental impact statement will be drawn up and made public later this year. Commercial timber crews will be hired and given detailed direction. And although some logs will be sold and the money used to offset costs, the goal will not be profit, but rather ecological restoration, he said.

A similar project has been underway for the past few years at San Vicente Redwoods Preserve, an 8,300-acre property in rural Santa Cruz County near the town of Davenport. The land was purchased for $30 million in 2011 by four environmental groups — the Peninsula Open Space Trust, Save the Redwoods League, Trust for Public Land and Land Trust of Santa Cruz County. Since then, they have allowed roughly 350 acres that were logged years ago to be thinned again, raising about $500,000 that has funded stream restoration, a public access plan and other work on the property. A new logging plan being drawn up this year aims to restore previously logged areas of the property.

Some environmental groups are OK with the trend.

“There is a need for restoration. What they are trying to do is exciting,” said Tom Wheeler, executive director of EPIC, the Environmental Protection Information Center, in Arcata, which fought commercial logging plans at Headwaters Forest in Humboldt County during the 1990s. “Honestly, it is a little bit of an experiment. There is only one way to create old growth redwoods and that is with time. If we can kick start the process a little bit, then we are all in favor of that.”